It is presently well known to provide for liquid infusion into a living body by providing a container, acting as a reservoir for holding liquid to be infused and which is connected to the body via a conduit in which pressure supplying the fluid is created by either a gravitational pressure head or by pressure generation means.
In these systems there are three main factors controlling the actual infusion rate of the liquid to be infused into a patient. The first is the height that the liquid container is held relative to the outlet and the second factor is the degree of back pressure which is experienced as the liquid enters the patient. It is a disadvantage in such a simple arrangement that the back pressure can provide significant changes in flow rate and this can be altered almost casually without intention by the patient perhaps rolling over in bed or simply changing to a more comfortable position. A third factor is the viscosity of the fluid being infused. The viscosity can be changed due to temperature variation or change of fluid. As fluids have different viscosities fluid flow rate changes of up to 8% can be caused by this difference alone.
Furthermore, it is necessary on many occasions to keep the flow rate of the liquid within selected limits and this becomes either very difficult or impossible with the simple gravitationally actuated device of the type discussed.
Thus, in the past it has been very difficult to provide a fluid for infusion into a body at a constant flow rate and to ensure that a selected quantity of the fluid is infused into the body at any given time and with a high degree of accuracy and without the unwanted effects of back pressure. The present invention seeks to improve administration sets used for the purpose of infusing fluids into the human body by providing a flow controller which is adapted to be used as an attachment to the administration set or alternatively to be integral with an administration set.